Ecological suitability modeling for anthrax in the Kruger National Park, South Africa

The spores of the soil-borne bacterium, Bacillus anthracis, which causes anthrax are highly resistant to adverse environmental conditions. Under ideal conditions, anthrax spores can survive for many years in the soil. Anthrax is known to be endemic in the northern part of Kruger National Park (KNP) in South Africa (SA), with occasional epidemics spreading southward. The aim of this study was to identify and map areas that are ecologically suitable for the harboring of B. anthracis spores within the KNP. Anthrax surveillance data and selected environmental variables were used as inputs to the maximum entropy (Maxent) species distribution modeling method. Anthrax positive carcasses from 1988–2011 in KNP (n = 597) and a total of 40 environmental variables were used to predict and evaluate their relative contribution to suitability for anthrax occurrence in KNP. The environmental variables that contributed the most to the occurrence of anthrax were soil type, normalized difference vegetation index (NDVI) and precipitation. Apart from the endemic Pafuri region, several other areas within KNP were classified as ecologically suitable. The outputs of this study could guide future surveillance efforts to focus on predicted suitable areas for anthrax, since the KNP currently uses passive surveillance to detect anthrax outbreaks.引发炭疽病的土壤传播性细菌——炭疽芽孢杆菌（Bacillus anthracis）的芽孢，对恶劣环境条件具有极强抗性。在理想环境条件下，炭疽芽孢可在土壤中存活多年。已知炭疽病在南非（South Africa, SA）境内的克鲁格国家公园（Kruger National Park, KNP）北部地区呈地方性流行，偶有疫情向南扩散。本研究旨在识别并绘制克鲁格国家公园内适宜炭疽芽孢杆菌芽孢存活的生态适宜区域。研究以炭疽监测数据与筛选得到的40项环境变量为输入，采用最大熵（Maxent）物种分布建模方法。本研究利用1988—2011年间克鲁格国家公园内的597具炭疽阳性动物尸体（n=597）与总计40项环境变量，预测并评估了各环境变量对克鲁格国家公园内炭疽发生适宜性的相对贡献。对炭疽发生贡献度最高的环境变量依次为土壤类型、归一化植被指数（normalized difference vegetation index, NDVI）与降水量。除地方性流行的帕富里（Pafuri）地区外，克鲁格国家公园内另有多处区域被归类为生态适宜区域。鉴于克鲁格国家公园目前采用被动监测手段检测炭疽疫情，本研究结果可为未来将监测工作聚焦于预测的炭疽适宜发生区域提供指导。